Systems and methods for testing conductive members employing electromagnetic back scattering

ABSTRACT

A system or method of analyzing a conductive member for the presence an anomaly. A test source signal is applied to a first test location on the elongate conductive member remote from the corrosion to cause the test source signal to travel along the pipe through the anomaly. At least one test return signal caused by the test source signal traveling through the anomaly is detected. The at least one test return signal for characteristics associated with the anomaly. Optionally, a perturbation may be applied to the elongate conductive member to place the conductive member in a perturbed state in which the electromagnetic characteristics of the conductive member at the anomaly are altered. The test source signal is applied to the first test location when the conductive member is in the perturbed stated.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/840,488 filed May 6, 2004, which claims priority of U.S.Provisional Patent Application Services No. 60/468,626 filed May 6,2003, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to testing systems and methods forconductive members and, more specifically, to systems and methods fordetecting anomalies such as corrosion at remote locations on insulated,shielded metallic pipes.

BACKGROUND OF THE INVENTION

Corrosion of steel pipes can degrade the structural integrity of thepipeline system. In some pipeline systems, the metallic pipe isinsulated with a urethane foam covering and protected by an outermetallic shield. In other pipeline systems, the metallic pipe is buried.For insulated, shielded pipes, visual inspection is impossible withoutphysically removing the insulation and outer shield. For buried pipes,visual inspection is also impossible without excavating the pipe.

Current methods of testing pipe without removing the insulation andouter shield or excavation include acoustic wave propagation through themetal and x-ray radiography. However, acoustic wave propagation andx-ray radiography are only applicable to a single point location or overa short distance.

The need thus exists for improved systems and methods for testing foranomalies on a length of pipe without excavation or removing theshielding and insulation.

SUMMARY OF THE INVENTION

The present invention may be embodied as a system or method of analyzinga conductive member for the presence an anomaly. A test source signal isapplied to a first test location on the elongate conductive memberremote from the corrosion to cause the test source signal to travelalong the pipe through the anomaly. At least one test return signalcaused by the test source signal traveling through the anomaly isdetected. The at least one test return signal for characteristicsassociated with the anomaly. Optionally, a perturbation may be appliedto the elongate conductive member to place the conductive member in aperturbed state in which the electromagnetic characteristics of theconductive member at the anomaly are altered. The test source signal isapplied to the first test location when the conductive member is in theperturbed stated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 1B are somewhat schematic views of systems for testing foranomalies on a pipe system;

FIGS. 2-14 are graphs plotting data obtained using the systems describedin FIGS. 1, 1B, and 15.

FIGS. 15 and 16 are somewhat schematic views of systems for testing foranomalies on a pipe system;

FIGS. 17-19 are partial cutaway views depicting an example probe systemthat may be used by the testing system of FIG. 16;

FIG. 20 is a graph plotting data obtained using the system depicted inFIG. 16; and

FIG. 21 is a schematic block diagram depicting a test system thatdemonstrates that corroded pipe has measurable DC nonlinear resistance;

FIG. 22 is a plot of resistance in ohms versus time illustrating datacollected using the test system depicted in FIG. 21;

FIG. 23A-C are schematic block diagrams depicting example configurationsof a system for conducting time domain impedance analysis of an elongateconductive member in accordance with the principles of the presentinvention;

FIG. 24 is plot of change of impedance versus distance obtained bymeasuring at a first end of the elongate conductive member analyzed bythe system of FIG. 23B demonstrating the remote detection of corrosionnonlinearity activated using an external DC bias supply;

FIG. 25 is plot of change of impedance versus distance obtained bymeasuring at a second end of the elongate conductive member analyzed bythe system of FIG. 23C demonstrating the remote detection of corrosionnonlinearity activated using an external DC bias supply; and

FIG. 26 is a plot four different traces of voltage versus time obtainedusing the system of FIG. 23 comparing three different bias conditionswith a calibration marker.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1 of the drawing, depicted therein is anexample measurement setup 20 constructed in accordance with, andembodying, the principles of the present invention. The examplemeasurement system 20 is designed test for anomalies in a pipelinesystem 30 comprising a conductive pipe 32, a conductive outer shield 34,and insulation 36. The pipe 32 and outer shield 34 are typicallymetallic, and the insulation 36 is typically urethane foam. The pipe 32is typically centered in the shield 34 by the insulating layer 36. Thepipeline system 30 thus effectively forms a constant impedance coaxialtransmission line capable of propagating electromagnetic waves in thetransverse electromagnetic (TEM) mode.

Illustrated at 40 in FIG. 1 is an anomaly such as an area of corrosionon the outside of the pipe 32. The anomaly 40 can affect the wavetransmission by the pipeline system 30. In particular, the impedance ofa coaxial transmission line is a function of the diameter of the innerand outer conductor and the dielectric constant of the material betweenthem.

In the context of the pipeline system 30, the anomaly 40 can change thephysical properties of the pipe 32, which in turn can affect theimpedance of the system 30. For example, if the anomaly 40 is corrosion,the corrosion may thin the wall of the pipe 32 as shown at 42 in FIG. 1,thereby changing the impedance of the system 30. Corrosion can alsospread into the insulating layer 36 as shown at 44 in FIG. 1, which canalso affect the impedance of the pipeline system 30 by modifying thedielectric constant between pipe 32 and the shield 36. These changes inimpedance can cause electromagnetic pulses propagating along the coaxialtransmission line formed by the pipeline system 30 to reflect backtoward the source of the electromagnetic wave or pulse.

FIG. 1 further illustrates an example test system 50 for detectinganomalies such as the anomaly 40 along the pipeline system 30. Theexample test system 50 comprises a source system 52, a sensor system 54,and a marker system 56. The source system 52 applies an electromagneticpulse signal to the pipeline system 30. The sensor system 54 detectselectromagnetic waves propagating along the pipeline system 30. Themarker system 56 allows the test system 50 to be calibrated for aparticular pipeline system 30 under test.

The example test system 50 tests the quality and integrity of metallicpipelines using the backward reflection of an electromagnetic impulsewave propagating along the pipe. In particular, the test system 50propagates an electromagnetic impulse along the pipe and observesreflections from corrosion and other features which might affect theintegrity of the system. The test system 50 thus allows improvedelectromagnetic inspection without removal of the entire shield and/orinsulation. The test system 50 further allows testing of completesegments of pipe over extended lengths. Given the foregoing generalunderstanding of the present invention, the example test system 20 willnow be described in further detail.

The example source system 52 comprises a launcher 60, a matchingresistor 62, a coaxial cable 64, and a pulse generator 66. The launcher60 is used to excite waves which propagate in both directions along thepipe 32. In particular, the example launcher 60 makes electrical ohmiccontact with the pipe 32 to cause waves to propagate in the insulation36 between the pipe 32 and the outer shield 34. Exhibit A attached toProvisional Application Ser. No. 60,468,626 depicts details of oneexemplary embodiment of the example launcher 60 described herein.

The matching resistor 62 is used to prevent reflected energy fromtraveling back toward the source system 52 through the coaxial datacable 64. The value of the matching resistor 62 is chosen to terminatethe coaxial cable 64 in its characteristic impedance.

The pulse generator 66 forms the source of electromagnetic energy whichexcites the electromagnetic waves in the pipe system 30. The pulsegenerator 66 generates electromagnetic energy in any one of a numberforms. As examples, the pulse generator 66 could provide a 500 Voltnegative impulse with a duration of 2 nanoseconds or a step waveformwith similar characteristics.

The coaxial cable 64 transmits the voltage pulses generated by the pulsegenerator 66 to an injection point 68 on the pipe 32 and shield 34. Theapplication of the voltage pulses to the injection point 68 causes acurrent pulse to be launched in both directions from the injection point68. The electromagnetic impulse propagates away from the injection point68 in both directions in the space between the pipe 32 and the shield34.

The sensor system 54 detects reflections from the anomaly 40 or otheranomalies on the pipe system 30. The sensor system 54 comprises anelectric field sensor 70, a measurement device 72, and a coaxial line74. The electric field sensor 70 is a differentiating electric fieldsensor that detects electromagnetic waves by capacitive coupling of theelectric field. One example of the electric field sensor 70 is known inthe art as a D-dot probe. When subjected to a local electric field atthe measurement point, a D-dot probe responds with an output voltagewhich is proportional to the time rate of change of the local electricfield at the measurement point. The example D-dot probe used as theelectric field sensor 70 consists of a small capacitive element whichcouples to the local electric field.

One example of an appropriate electric field sensor 70 is depicted inExhibit B attached to Provisional Application Ser. No. 60,468,626. Theoutput signal from the electric field sensor 70 is coupled to themeasurement device 72 using the coaxial line 74. The measurement device72 is preferably an oscilloscope or digital transient data recorder suchas a Tektronix 3054 digital oscilloscope. The measurement device 72records a signal which is proportional to the time derivative of theelectric field at the location of the electric field sensor 70.

In use, the sensor system 54 will detect a first pulse as the excitingwave passes the electric field sensor 70. Later pulses are seen ifsignals reflect from variations in coaxial transmission line impedance,such as those caused by an anomaly 40 such as an area of corrosion onthe pipe.

The signals recorded on the measurement device 72 can be numericallyintegrated to recover the local electric field waveform at themeasurement point of the electric field sensor 70. Such a waveform willshow an initial pulse coming from the source system 52, followed byreflections coming from anomalies on the line.

One object of the invention is to isolate reflections which come fromthe left or the right side of the injection point so that locations ofanomalies can be identified unambiguously. Reflections will be seen fromanomalies both to the right and to the left from the injection point. Toseparate these, the electric field sensor 70 may be moved to separatefirst, second, and/or third sensor locations 76 a, 76 b, and 76 c whichcould, for example, be separated by a distance of 5 feet. Alternatively,three separate probes and/or measurement systems may be used, one foreach of the sensor locations. Timing of the wave arrival of the incidentand reflected pulse at the three separate locations 76 a, 76 b, and 76 callows both the distance and the direction of the anomaly to bedetermined by simple wave propagation calculation. Exhibit D attached toProvisional Application Ser. No. 60,468,626 illustrates and describesone example of the process of moving the sensor 70 to different sensorlocations.

In addition, the three recorded signals from three separate locationscan be time shifted by a fixed delay to bring each reflection from theright hand direction into time coincidence. Reflections from the leftwill not coincide. When added together the three time-shifted waveformsgive a unidirectional measurement looking to the right. A secondintegration of the recorded data can give additional information aboutthe magnitude and longitudinal extent of the measured anomalies.

The wave impedance of a coaxial transmission line is well known todepend on the spacing of the inner conductor and outer conductor and thedielectric properties of the insulating media separating them. TheApplicant has discovered that the wave impedance of the pipeline system30 is similar to the wave impedance of a coaxial transmission line.

Referring initially to conductor spacing, a change in the conductorspacing causes a corresponding change in the impedance. In the contextof the pipe system 30, if the effective diameter of the pipe 32 (theinner conductor) is increased, the conductor spacing decreases, yieldinglower wave impedance and causing a reflection with polarity opposite tothe source polarity. If the effective diameter of the pipe 32 decreases,the wave impedance is increased, causing a reflection with the samepolarity as the source.

The insulating media between the inner and outer conductors also has aneffect on wave impedance. In the context of the pipe system 30, if thedielectric constant of the insulating layer 36 is increased by thepresence of moisture or higher density foam, the local wave impedancewill be lowered, and a reflection with polarity opposite to the sourcewill be generated.

The presence of corrosion products or other material with highdielectric constant in the space between the pipe and the outer shieldwill also cause a reflection with polarity opposite to the sourceimpulse waveform. Conversely, a gap in the shield or a region of missinginsulation will result in higher wave impedance, and this higher waveimpedance will reflect a signal with the same polarity as the source. Inaddition, the duration of the reflected signal corresponds with thelength over which the increased dielectric material occurs.

Using the test system 50, all of these factors can be used to determinethe presence, extent, and location of anomalies along the pipe system30.

The marker system 56 is used to calibrate or set a reference for thetest system 50. The marker system comprises a pipe engaging member 80, ashield engaging member 82, and a shorting conductor 84. One example of amarker system 50 is shown in Exhibit C attached to ProvisionalApplication Ser. No. 60,468,626.

The marker system 56 is placed at a known point on the pipe 32. Themarker system 56 forms a direct short circuit connection between thepipe 32 and the shield 34. The exemplary pipe engaging member 80 andshield engaging member 82 magnetically attach to the pipe 32 and shieldmember 34, respectively. The shorting conductor 84 is typically a lowinductance braid or strap conductor that connects the pipe engagingmember 80 to the shield engaging member 82.

The marker system 56 provides a high quality connection between the pipe32 and shield 34 which will reflect a known quantity of energy backtoward the source system 52. The marker is used to calibrate the system50 by determining a propagation speed of propagation in the particularinsulation used as the insulating layer 36. Knowledge of wavepropagation speed is used for range calibration. A wave speed of 1.07nanoseconds per foot is typically measured for the urethane foaminsulation used on the Alaska pipeline.

The marker system 56 also allows verification of proper operation of thesystem 50 by providing a known reflection signal. The level ofattenuation of the reflected pulse from the marker system 46 gives anoverall indication of the quality of the insulation forming theinsulating layer 36 and also can reveal defects in the outer shield 34.

Referring now to FIGS. 2-14, depicted therein are graphs showing datacollection and analysis using the principles of the present invention.The Ddot antenna, as it is used in this application, provides thederivative of the source field as it propagates and reflects in thespace between the pipe and the shield. Therefore, the unaltered signal,propagating and reflecting along the pipe, will contain high frequencyinformation which, often will hide or mask information concerning thephysical condition of the pipe. FIG. 2 illustrates raw data collectedusing the Ddot antenna as described herein as the electric field sensor70. Raw data as shown in FIG. 2 is beneficial in analyzing the pipelinesystem for very small flaws determined by a combination of pulse risetime, pulse width, and bandwidth of the detection hardware.

Integration of the raw data may more clearly illustrate the effect ofthe propagation path on the injected pulse. Since the Ddot antennasensor differentiates the injected pulse, this integration approximatelyreproduces the injected pulse, smoothes out some of the very highfrequency information in the raw data, and makes it easier to see largeranomalies that more closely correlate to pipeline anomalies that are ofinterest to the pipeline operating company. The chart depicted in FIG. 3is an example of how the data appears after the first integration step.

To observe still another family of anomalies, one more level ofintegration may be used. The second integral of the raw Ddot dataillustrates how the pipeline would respond to a step function, whileusing an impulse type pulse generator or pulser. The second integral ofthe data provides some additional smoothing, is less sensitive to smallanomalies, and provides better visibility of larger anomalies. FIG. 4illustrates how the data appears after the taking of the second integralof the raw data.

The data may also be time shifted to determine exactly what directionthe anomalies come from and where they are located. FIG. 5 illustratesthe time shifting of the data after the first integration step. FIG. 1Battached hereto is a somewhat schematic diagram illustrating asimplified layout of the particular pipeline configuration that waspresent where this data was acquired.

FIG. 5 illustrates five features identified using reference charactersA, B, C, D, and E for each Ddot probe location. The first arrival of thepulse from the launcher is at position “A”. Features “B”, “D”, and “E”in general are located to the left of the launcher, because they are nottime shifted. Note however, that the feature at “C” is time shifted inthe data as the Ddot probes are moved to the right. The anomalies to theright of the launcher will appear earlier in time as the Ddot is movedto the right. For this particular test, the pipe segment going under theroadway and through a casing lies to the right of the probes and is thesegment of most interest.

FIG. 5 thus allows us to see the right side data properly oriented bytime shifting probe positions #1 and #2 with respect to #3 as shownabove. In this view, it is clear that the feature at “C” is inhorizontal alignment at all three Ddot probe positions, the firstarrival pulses at “A” and the features at “B”, “D”, and “E” are now notaligned. The differences are not quite as obvious because of all thehigh frequency in the raw data, but they can still be seen in closeinspection of that data shown in FIG. 6.

FIG. 7 illustrates the time shifted double integral. FIG. 7 shows thenormal double integral data. Note again that only location “C” is timeshifted to the left, indicating that it is physically located to theright of the Ddot probes. When the data is time shifted with respect toDdot location #3, all locations “C” are horizontally aligned, while “A”,“B”, “D”, and “E” are no longer aligned.

One additional step can be taken to enhance the data. The time shifteddata at each probe location may be summed and divided by the number ofsensor locations 76, which in this case is equal to three.

FIG. 8 shows the summation of the time shifted waveforms for the rawdata. FIG. 9 shows the summation of the time shifted waveforms for thefirst integral of the raw data. FIG. 10 illustrates the summation of thetime shifted waveforms for the first integral of the raw data. FIG. 11illustrates the summation of the time shifted waveforms for the secondintegral of the raw data. FIG. 12 compares the time shifted summation ofthe raw data, the first integral of the raw data, and the secondintegral of the raw data. FIG. 13 compares the time shifted sum of thesecond integral of the raw data with the second integral of the rawdata. Note, sequentially, how the information in the test segment to theright of the Ddot probes becomes clear.

The anomaly indicated at 100 in the data depicted in FIGS. 3-5, 7, 10-13was excavated after the test, and corrosion with 60% metal loss wasfound at the exact location indicated by the data.

FIG. 14 illustrates the process of using the marker system 56 to helpcorrelate characteristics of the graphs with the pipe under test. Thesensor 70 used by the test system 50 may take the form of aself-integrating probe as will be described below and in Exhibit Eattached to Provisional Application Ser. No. 60,468,626. Very low levelsignals, due to improper grounding, or baseline shifts in theacquisition, can cause problems with the data that make it verydifficult to interpret. A self-integrating probe can enhance datacollection and overcome the problems described above.

In particular, a Ddot probe has been adapted to the tip of a TektronixFET probe, such as the P6243. Instead of a resistive voltage divider,this system becomes a capacitive voltage divider, and the output of theprobe is the first integral of the raw data. Pictures of the workingprototype are shown in Exhibit E attached to Provisional ApplicationSer. No. 60,468,626. In the device shown in that Exhibit E, the shortjumpers have been eliminated, and the probe interfaces to a much higheroutput Ddot with gold plated pins approximately ¼ inch from the pipejacket. The system shown in that Exhibit E significantly reduceselectrical noise sometimes associated with the resistive voltage dividerdesign. This improvement thus helps overcome the difficulties ofmaintaining laboratory quality measurement in a harsh environment.

In addition, shown in FIG. 15 is a modified test system 50 a in whichthe source system 52 uses a Ddot probe 90 as the launcher 60 to launchthe pulse onto the pipe 32. The pulse will be applied to the pipe usingthe Ddot probe 90 as the launcher 60 to inject the signal into the spacebetween the pipe 32 and the external shield 34.

Several advantages are obtained from the use of the Ddot probe 90 as thelauncher 60. First, the Ddot probe 90 need not be in resistive contactwith the pipe 32.

Another advantage of using a Ddot probe as a pulse launcher 60 is thatthe pulser 60 can be made an integral part of the launcher 60 with abuilt in rate generator. This enhances multi-port signal injectionwithout the need for additional signal cables or large battery packs. Invery close quarters, such as found in refineries and chemical processingplants, the process would be extremely portable and combined with someof the other improvements, the test results could be almost real time.

A Ddot probe detects the electric field and is omni directional. A Bdotprobe detects the magnetic field and is directional. A possibleimprovement over the use of a self integrating Ddot probe would be touse a Bdot probe, which would automatically detect the direction of theanomaly on the pipe. The use of a Bdot probe may be considered ahardware implementation of what is described above in software and mightresult in more accuracy, less training of personnel, and higher testproduction.

Referring now to FIG. 16, depicted therein is yet another exemplary testsystem 120 constructed in accordance with, and embodying, the principlesof the present invention. The test system 120 is shown testing a segment122 of insulated, shielded pipe 30 as described above.

As schematically shown in FIG. 16, the example segment 122 of pipe 30comprises first and second terminating assemblies 124 and 126 formed byfour terminating resistors 128. The terminating assemblies 124 and 126allow the segment 122 to simulate a longer pipe and do not form a partof the present invention. In the example segment 122 depicted in FIG.16, the segment 122 is approximately 100 feet long.

The test system 120 comprises a signal processing system 130 comprisinga probe 132 and a signal analyzer 134 connected by a cable 136. Theprobe 132 is arranged at a test location 138 spaced between the ends 122a and 122 b of the segment 122. In particular, the test location 138 isapproximately twenty-two feet from the first segment end 122 a andapproximately seventy-eight feet from the second segment end 122 b. Thetest location 138 and first and second segment ends 122 a and 122 b willbe referred to as points A, B, and C, respectively.

The example probe 132 functions as both a source of a pulse or series ofpulses applied to the pipe system 30 and as a sensor for receiving anyreflected pulses arising from features or anomalies of the pipe system30. The sensor portion of the probe 132 transmits any such reflectedpulses to the signal analyzer 134 through the cable 136. The probe 132further generates a trigger pulse that is sent to the signal analyzer134 through the cable 136 to facilitate analysis of the reflectedpulses.

Referring now to FIGS. 17-19, depicted in detail therein is an exampleembodiment of the probe 132 and an attachment system 140 for detachablyattaching the probe 132 to the pipe 30.

As shown in FIG. 17, the example attachment system 140 comprises a basemember 142, a seal 144, a cap member 146, and an O-ring 148. The basemember 142 defines a flange portion 142 a and a mounting portion 142 b.The mounting portion 142 b defines a passageway 150. The passageway 150defines a first threaded surface 152, while the cap member 146 defines asecond threaded surface 154. The cap member 146 may be detachablyattached to the base member 142 using the threaded surfaces 152 and 154,but other attachment systems can be used.

The flange portion 142 a of the base member 142 is attached to theshielding 34 by screws, bolts, adhesives, or the like. A shield opening156 is formed in the shielding 34 to allow access to the pipe 32 throughthe passageway 150. The seal 144 may be formed, as examples, by aseparate gasket or a layer of hardened adhesive between the base member142 and shielding 34. The mounting portion 142 b of the base member 142defines the passageway 150 and extends outwardly away from the pipesystem 30.

In a first configuration, the cap member 146 is detachably attached tothe base member 142 such that the cap member 146 closes the passageway150; the seal 144 and O-ring 148 inhibit entry of moisture into the pipesystem 30 through the shield opening 156 in this first configuration. Ina second configuration, the cap member 146 is detached from the basemember 142 such that pipe 32 is accessible through the passageway 150and the shield opening 156.

As perhaps best shown in FIG. 18, the probe 132 comprises a housing 160,electronics 162, a pipe terminal 164, a cable terminal 166, andalignment projections 168. The electronics 162 are mounted within thehousing 160. The pipe terminal 164 is supported at one end of thehousing 160. The cable terminal 166 is also supported by the housing160. The pipe terminal 164 and cable terminal 166 are electricallyconnected to the electronics 162.

The housing 160 is sized and dimensioned to be inserted at least partlythrough the passageway 150 and the shield opening 156. Although othershapes may be used, the passageway 150, shield opening 156, and housing160 are at least partly cylindrical in the example signal processingsystem 130.

To use the signal processing system 130, the probe housing 160 isinserted through the passageway 150 and shield opening 156 until thepipe terminal 164 comes into contact with the pipe 32. The alignmentprojections 168 also engage the pipe 32 to center the pipe terminal 164on the curve of the pipe 32. Additionally, a fixing mechanism may beused to fix the position of the probe housing 160 relative to the basemember 142 when the pipe terminal 168 is in a desired relationship withthe pipe 32. For example, a set screw or the like may extend through themounting portion 142 b of the base member 142. Rotating the set screwrelative to the base member 142 displaces the set screw towards thehousing 160 to force the housing 160 against the threaded surface 152 tosecure the housing 160 relative to the base member 142.

The electronics 162 are then activated to apply an electrical pulse tothe pipe 32 through the pipe terminal 164. Applied signals will thuspropagate in both directions away from the test location 138. The pulsegenerator may take the form of a simple timing circuit that generates anelectrical pulse; the electrical pulse may take on a number of forms,but the example electronics 162 generates a step function waveform. Theelectronics 162 further comprise an impedance matching resistor arrangedbetween the pulse generator and the pipe terminal 164.

As described above, the applied signals traveling away from the testlocation 138 may encounter anomalies and features of the pipe system 130that will cause at least one reflected signal to travel back towards thetest location 138. The probe 132 is further capable of detecting atleast some of the reflected signals as they pass through the testlocation 138. In particular, the probe 132 may directly sense thereflected signals through ohmic contact between the pipe terminal 164and the pipe 32. In this case, a simple resistive divider probe may beconnected to the pipe terminal 164. Alternatively, a Ddot probe may bearranged within the housing 160 adjacent to the pipe terminal 164 tointroduce reflected signals into and/or sense reflected signals in thepipe system 30.

In any case, the electronics 162 contains circuitry as necessary tointroduce the applied signals into the pipe 32 and sense the reflectedsignals traveling through the test location 138. The reflected signalssensed by the electronics 162 are applied to the cable terminal 166 fortransmission to the signal analyzer 134. The electronics 162 further maygenerate a trigger signal corresponding to the generation of theelectrical pulses applied to the pipe 32. The trigger signal is alsoapplied to the cable terminal 166 to facilitate analysis of thereflected signals by the signal analyzer 134.

Referring now to FIG. 20, depicted therein is a graph 170 representingthe reflected signals received using the signal processing system 130 onthe pipe segment 120 illustrated in FIG. 16. The graph 170 containsthree traces 170 a, 170 b, and 170 c.

The trace 170 a depicts the signal measured by the signal analyzer 134with the standard test system as depicted in FIG. 16 (i.e., fourterminating resistors 128 connected to each end 122 a and 122 b). Thestandard test system generally corresponds to a good pipe of infinitelength. After an initial steep drop and rise in the time intervalrepresented by approximately 0 to 3 on the X-axis, the trace 170 abegins a gradual, relatively featureless decline.

The trace 170 b illustrates the signal measured by the signal analyzer134 with one of the terminating resistors 128 shorted on the first end122 a of the segment 122. The trace 170 b is similar to the trace 170 ain the time interval represented by approximately 1-15 of the X-axis. Inthe time interval represented by approximately 15-30 on the X-axis, theslope of the trace 170 b increases and becomes positive. In the timeinterval represented by approximately 30-130, the trace 170 b generallydeclines in a manner similar to the trace 170 a but exhibits change inslope similar to those associated with an oscillation. A line 172 inFIG. 20 illustrates that the scale associated with the X-axis has beenselected such that the initial rise in the slope of the trace 170 bcorresponds to the location 22 feet away.

The trace 170 c illustrates the signal measured by the signal analyzer134 with one of the terminating resistors 128 shorted on the second end122 b of the segment 122. The trace 170 c is similar to the trace 170 ain the time interval represented by approximately 1-75 of the X-axis. Inthe time interval represented by approximately 75-83 on the X-axis, theslope of the trace 170 c increases and becomes positive. In the timeinterval represented by approximately 83-130, the trace 170 c generallydeclines in a manner similar to the trace 170 a but exhibits change inslope similar to those associated with an oscillation. A line 174 inFIG. 20 illustrates that the scale associated with the X-axis has beenselected such that the initial rise in the slope of the trace 170 ccorresponds to the approximately location 78 feet away.

Analyzing both traces 170 b and 170 c in the context of the scaleselected for the X-axis illustrates that the anomalies in the traces 170b and 170 c generally correspond to the anomalies in the pipe segment122 at the first and second ends 122 a and 122 b thereof, respectively.The test system 120 thus effectively determines differences in impedanceintroduced in the test segment 122. The Applicants believe that the testsystem 120 can thus be used to determine differences in impedance causedby anomalies in a pipe system such as corrosion.

In addition, signal processing techniques described above with referenceto FIGS. 2-14 may also be applied to the traces 170 b and 170 c. Forexample, subtracting the trace 170 b from the trace 170 a will result ina series of spikes, with the first such spike being associated with theanomaly at the first end 122 a of the pipe segment 122. Additionalsignal processing techniques might allow the traces to be examined byrelatively low-skilled technicians or even automated such that thedetection of anomalies may be performed by a computer.

The example pipe segment 122 depicted in FIG. 16 is a very simple caseof a straight pipe with no features such as terminations, corners,changes in diameter, or the like. In the real world, the pipe system 30may be used to form a long pipeline or an extensive network ofinterconnected pipes at a manufacturing site. In such a larger pipesystem, features of the pipe in good condition may cause reflectedsignals that may not be easily distinguishable from reflected signalsgenerated by anomalies, such as corrosion, associated with failed orfailing pipe.

To facilitate the recognition of features associated with failed offailing pipe, traces may be generated for pipe in known good conditionat one point in time and compared with traces generated at one or morelater points in time. Changes in the traces over time can be monitored.If these changes fall outside predetermined parameters, the pipe undertest can be checked for failure at locations associated with changes inthe trace.

Also, to test discrete portions of the pipe system 30 in a largersystem, the probe 132 may be detachably attached in sequence to one ormore discrete test locations in the pipeline or network of pipes. FIGS.17-19 describe one possible attachment system 140 that may be used forthis purpose. Alternatively, probes like the probe 132 may bepermanently attached to one or more test locations located along thepipeline or throughout the pipe network. In this case, the probe 132 maybe provided with an access port, memory, and/or telemetry systems forsimplifying the process of obtaining data.

Yet another example of a system and method of remotely analyzing anelongate conductive member for anomalies will now be described withreference to FIGS. 21-26. In particular, depicted in FIG. 23 is anexample test system 220 that may be used to determine the presenceand/or location of anomalies along an elongate conductive member 222.

Like the systems and methods described above, the test system 220employs the backward reflection of an electromagnetic pulse wavepropagating along the elongate conductive member 222. However, theApplicants have recognized that, for certain anomalies, theeffectiveness of the systems and methods of the type generally describedabove can be improved by perturbing the elongate conductive member 222as the electromagnetic pulse is applied thereto.

Certain types of anomalies are typically of more interest than othertypes of anomalies. In the following discussion, the term “spuriousanomalies” will refer to anomalies in an elongate conductive member thatare not of interest. Backscattered electromagnetic energy from spuriousanomalies can obscure backscattered electromagnetic energy fromanomalies of interest such as corrosion of a pipe member.

In the example test system 220 described with respect to FIGS. 21-26,the elongate conductive member 222 is a pipe member 230 forming part ofa pipe system 232. The pipe member 230 may be buried or unburied orcased or uncased. The pipe system 232 may comprise or be influenced bypipe components such as flanges, insulation, and shielding,environmental conditions such as dirt and ground water, and anomalies onthe pipe such as iron oxide (rust).

The example pipe member 230 under test is a 4-inch direct buried pipetwo-hundred sixteen feet in length. The pipe member 230 defines firstand second ends 234 and 236. First and second pipe portions 240 and 242are located seventy-five and fifty feet, respectively, from the secondend 236. In the example pipe system 232, the pipe portions 240 and 242are known to be corroded. The pipe system 232 further defines first,second, and third test locations 244, 246, and 248 at which testequipment may be located as will be described in further detail below.The first and second test locations 244 and 246 are arranged at thefirst and second ends 234 and 236 of the pipe, while the third testlocation 248 is located along the pipe between the first and second ends234 and 236.

The example third test location 248 happens to be located seventy-twofeet from the second end, or between the first and second pipe portions240 and 242. The physical relationship between third test location 248and the corroded pipe portions 240 and 242 need not be predetermined oreven known in advance.

The corroded pipe portions 240 and 242 would be considered anomalies ofinterest in the context of the pipe member 230. The following anomaliesmight also be considered anomalies of interest: stress cracks, depositsof magnetic oxides (rust), metal fatigue, improper welds, and regions ofactive electrolysis that have not yet progressed to visible corrosion.In the pipe system 232, spurious anomalies might include non-structuraldents and, in the case of direct buried pipe, changes in soilcomposition, roots, debris, rocks, ground water.

The Applicants have recognized that the electromagnetic properties ofcertain anomalies of an elongate conductive member 222 are nonlinear,and this fact can be used to determine whether backscatteredelectromagnetic energy is caused by anomalies of interest or by spuriousanomalies. Anomalies having nonlinear electromagnetic properties will bereferred to herein as nonlinear anomalies, and certain nonlinearanomalies are anomalies of interest.

The Applicants have further recognized that perturbing the pipe member230 by, for example, modifying the electric or magnetic field of thepipe member 230 modifies the electromagnetic properties of the pipemember 230 at the location of nonlinear anomalies. The modifiedelectromagnetic properties of the pipe member 230 at the location of thenonlinear anomalies result in differences in the backscatteredelectromagnetic energy signals reflecting from the nonlinear anomalies.These differences can be detected and used to determine both thepresence of the nonlinear anomaly and, in conjunction with othercharacteristics of the pipe system 232 that will be described furtherbelow, the location of the nonlinear anomaly.

In the specific case of corrosion, electrolytic activity associated withactive corrosion can give nonlinear resistance. For direct buried pipein contact with moist earth, the surface resistivity in regions ofactive corrosion can vary with the applied electric field in a nonlinearmanner; that is, the ratio of voltage-to-current is not a constant. Inthis case, the perturbing voltage modifies the local impedance directlyby changing the pipe-to-soil resistance at the site of active corrosion.Changes in pipe-to-soil resistance at the site of active corrosion allowthe corrosion to be detected in buried pipes from a remote location.

In addition, areas of active corrosion can be located by measuringtime-of-flight for those returns that change when the perturbation ischanged. In this context, an electromagnetic pulse, referred to hereinas the source pulse, is applied to the conductive member 222 such thatthe pulse travels through anomalies on the conductive member. Theanomalies cause a portion of the electromagnetic energy of the sourcepulse to be reflected back along the conductive member. The reflectedenergy will be referred to herein as the return signal.

In the case of a bias current applied to a direct buried pipe, theresponse of the nonlinear properties in regions of corrosion can bedelayed in time by several seconds from the application of theperturbing field. This delay for polarization and depolarization tooccur can be used to isolate areas of active corrosion. The charge timefor polarization and decay time for depolarization depend on the degreeand type of corrosion. Various sources of corrosion can be identified byobserving changes in the backscattered electromagnetic signal after theperturbing field is reversed, turned-on, or turned-off. In addition, thepolarization and depolarization times were different for corroded andnon-corroded pipe.

The perturbation applied to the elongate conductive member 222 can beformed by methods other than simply applying a voltage or current to theconductive member. For example, a magnet held in proximity to theconductive member may perturb the conductive member at the anomaly.

The Applicants further recognized that the resistance of corroded pipehas a nonlinear current-voltage relationship that is quite differentfrom the current-voltage relationship of clear, un-corroded conductivemembers. This difference allows return signals from anomalies ofinterest to be identified in the presence of return signals fromspurious anomalies.

The return signals may further be processed using one or more dataprocessing techniques to determine which return signals are associatedwith anomalies of interest. One useful data processing technique is toobtain a plurality of sets of raw data for a particular set ofconditions and obtain an averaged set of raw data by averaging theplurality of individual sets of raw data.

As another example, a sequence of return signals may be detected for aparticular set of perturbation conditions. The sequence of returnsignals may be time-shifted and/or added to or subtracted from returnsgenerated for different sets of perturbation conditions. This techniquecan be used to separate return signals coming from opposite directionsalong the conductive member. In addition, the use of separate electricand magnetic field probes (D-Dot and B-Dot sensors) allow the directionof a return pulse to be determined based on a single point measurementwith time shifted subtraction.

Referring now more specifically to FIGS. 21 and 22, these figuresillustrate that the example anomalies at the corroded pipe portions 240and 242 alter the electromagnetic characteristics of the pipe member230. In particular, FIG. 21 depicts an example test set-up 250comprising a DC power supply 252, an ammeter 254, and a volt meter 256.A grounding electrode (anode) 258 is connected to one terminal of the DCpower supply 252 and may be formed by the anode of a conventionalcathodic protection system used to inhibit corrosion in pipe systems.The other terminal of the DC power supply 252 is connected to the thirdtest location 248 through the ammeter 254.

The DC power source 252 may take the form of a constant current orconstant voltage source that may be selectively switched on or off toperturb the elongate conductive member 222. If a bias current isemployed on the pipe, the resulting magnetic field can affect themagnetic properties of Ferro-magnetic iron-oxide (rust) at the corrosionsite. The magnetic permeability can change depending on the strength ofthe magnetic field caused by the externally applied current. The biascurrent thus creates a nonlinear magnetic response of the materialcaused by the applied perturbing field.

In a similar manner, a thin film coating of metallic oxide occurring atthe site of active corrosion in the presence of water can change thethickness of the film and resulting local capacitance due to thepresence of the electric field from an externally applied perturbingvoltage source. When either the local inductance or local capacitance ofa conductive member is changed, changes in the backscatteredelectromagnetic pulse signal can be observed. These changes can uniquelyidentify areas of corrosion.

The example DC power supply 252 is configured to apply a DC voltage tothe pipe member 230 at the third test location 248. The example DC powersupply 252 is a capable of applying DC voltages and currents to the pipemember 230 at different voltage and current levels and differentpolarities. When the DC power supply 252 is operated, the voltagemeasured by the volt meter 256 may be divided by the current measured bythe ammeter 254 to obtain the resistance of the pipe member 230.

Referring now to FIG. 22 of the drawing, depicted therein is the plot260 of pipe-to-soil resistance versus time obtained using the testsystem 250. The resistance was obtained by dividing the measured voltageby the injected current. The plot 260 comprises a first main portion 262associated with a first current level, a second main portion 264associated with a second current level, and a third main portion 266associated with a third current level. The polarity of the DC signal isaltered within each of the three main portions 262, 264, and 266 suchthat the plot further comprises first and second sub-portions 262 a,b,264 a,b, and 266 a,b within each of these plot portions 262, 264, and266.

Comparing the first sub-portions 262 a, 264 a, and 266 a of the first,second, and third main portions 262, 264, and 266 illustrates that theresistance as calculated from the measured current and voltage differswith differing magnitudes and polarities associated with thesesub-portions. Similarly, comparing the second sub-portions 262 b, 264 b,and 266 b of the main portions 262, 264, and 266 illustrates thatresistance is also different at the different current levels andpolarities associated with these sub-portions. Finally, comparing thefirst sub-portions 262 a, 264 a, and 266 a with the second sub-portions262 b, 264 b, and 266 b corresponding thereto illustrates that theresistance associated with the positive and negative polarities of theapplied DC signal is different.

The comparisons of the various portions of the plot 260 depicted in FIG.22 thus clearly indicate that the resistance of the pipe member 230 isnonlinear. Although only resistance data is plotted in FIG. 22, FIGS. 21and 22 thus illustrate that certain types of anomalies, including thecorrosion at locations 240 and 242, have unique, nonlinearelectromagnetic characteristics. In the case depicted and described withreference to FIGS. 21 and 22, the nonlinear electromagneticcharacteristics of the corrosion at locations 240 and 242 alter theresistance of the pipe member 230 at these locations 240 and 242 whenperturbed by the application of a DC voltage signal to the pipe member230.

Referring now to FIGS. 23A-C, the test system 220 depicted therein willbe described in further detail. The example test system 220 uses thephenomenon described with reference to FIGS. 21 and 22 to identify boththe presence and location of the anomalies at the locations 240 and 242on the pipe member 230.

The test system 220 comprises an exciting system 268 and a perturbationsystem 270. The exciting system 268 comprises a pulse source 272, asignal monitor 274, and a grounding screen 276. The perturbation system270 comprises a DC power supply 278.

The pulse source 272 is a pulse generator capable of generating anelectromagnetic pulse that may be applied to the conductive member 222.The example pulse source 272 may generate pulses of various magnitudesand shapes. For insulated shielded pipes, a pulse having an amplitude ofapproximately 500 volts and a pulse-width of approximately twonanoseconds may be used. For direct buried pipe, a step function voltagehaving a similar magnitude may be used. Other waveforms, such asunipolar, bipolar, and oscillatory waveforms, may be used depending uponthe environmental conditions. Swept frequency continuous wave sinusoidalfrequency sources may also be used to excite the conductive member 222.In this case, Fourier transform analysis may be used to convert thefrequency domain data to time domain data using FFT processing, eitherdirectly on a frequency domain network analyzer or on a computer.

The signal monitor 274 is configured to monitor and record a test signalV-MONITOR present at either the first test location 244 (FIG. 23C) orthe second test location 246 (FIGS. 23A-B). The signal monitor 274further operates based on a trigger signal TRG generated by the steppulse source 272.

The grounding screen 276 may be formed of any element, such as aphysical screen, wire, rod, or anode, capable of forming a counterpoiseor return conductor. The grounding screen 276 or other return conductorneed not extend the full length of the pipe. A short length of screenmesh lying on the ground directly above the end of the pipe from whichthe pulse is launched has been found to be sufficient. The returnconductor thus need only be of sufficient length to allow the pulsesource 272 to launch the electromagnetic pulse at either the first testlocation 244 (FIG. 23C) or the second test location 246 (FIGS. 23A-B).

Like the DC power supply 252 described above, the DC power supply 278 iscapable of applying DC voltages and currents to the pipe member 230 atdifferent voltage and current levels and different polarities.

The example test system 220 further comprises an optional firstgrounding electrode 280 and second grounding electrode 282. The firstgrounding electrode 280 may be formed by an electrode, wire, or stakeconnected between ground and the step pulse source 272, between groundand the grounding screen 276, or between ground and both the step pulsesource 272 and the grounding screen 276.

The second grounding electrode 282 is connected to one terminal of theDC power supply 278 and may be formed by the grounding terminal (anode)of a conventional cathodic protection system used to inhibit corrosionin pipe systems. The other terminal of the DC power supply 278 isconnected to either the first test location 244 (FIGS. 23A-B) or thesecond test location 246 (FIG. 23C).

In FIGS. 23A-C, the first and second ends 234 and 236 of the pipe member230 are labeled “NS” and “FS” and, in the following discussion, will bereferred to as the near side end and far side end, respectively, of thepipe member 230. The terms “near side” and “far side” are completelyarbitrary and are used by convention to identify the first and secondends of the particular pipe member 230 being tested by the test system220.

Referring initially to FIG. 23A, that figure illustrates that theconfiguration of the test system 220 depicted therein further comprisesa marker element 284 temporarily connected between the third testlocation 248 and the grounding screen 276. The marker element 284 maytake the form of a diode or short circuit connection temporarilyconnected to the pipe member 230 at a known location. If the physicallocation of the third test location 248 is known with respect to thepipe member 230, the marker element 284 may be used to calibrate thewave speed in the particular environment for the purpose of distancecalibration.

The use of a diode as the marker element 284 in connection with theelongate conductive member 222 also allows a nonlinearity to be remotelyintroduced into the system incorporating member 222 simply by applying aremote biasing DC voltage to turn the diode on or off.

Referring now to FIG. 23B, depicted therein is a configuration of thetest system 220 similar to that depicted in FIG. 23A, except that nomarker element 284 is connected to the third test location 248. In theconfiguration depicted in FIG. 23B, the test system 220 is usedgenerally as follows.

The pulse source 272 of the exciting system 268 selectively launches oneor more electromagnetic pulses from the far side 236 such that theelectromagnetic pulses propagate at least from the far side 236 towardsthe near side 234. When appropriate, the DC power supply 278 of theperturbation system 270 perturbs the conductive member by selectivelyapplying one or more DC voltage levels and/or polarities to theconductive member 222 at the near side 234. The signal monitor 274detects return signals caused by the backscatter of electromagneticpulses traveling along the conductive member 222. This backscatteroccurs when the pulses pass through anomalies on the conductive member222. In the example system 220, the return signals are voltage signals,and these voltage signals are correlated to conductor impedance at thelocation where the backscatter occurs.

The operation of the pulse source 272 is timed in relation to theoperation of the DC power supply 278 such that the signal monitor 274collects sets of raw data generated under different operating conditionsof the test system 220. For example, a first set of raw data may becollected with the DC power supply in an off position. A second set ofraw data may be collected after the DC power supply is operated to placea positive DC signal on the conductive member 222. A third set of rawdata may be collected after the DC power supply is operated to place anegative DC signal on the conductive member 222.

The sets of raw data may be analyzed directly for signatures associatedwith anomalies. The sets of raw data may additionally be processed andthen analyzed. For example, the first set of raw data may be subtractedfrom the second or third sets of raw data to illustrate differences inthe data associated with the perturbations caused by the perturbationsystem 270.

Referring now to FIG. 24 of the drawing, that figure contains a datatrace 290 of the data obtained using the test system 220 configured asshown in FIG. 23C. The data trace 290 represents samples of the returnsignals detected with the DC power supply off subtracted fromcorresponding return signals detected with the DC power supply set to apositive voltage. More specifically, the return signal detected with theDC power supply off is subtracted from the return signal detected withthe DC power supply applying a positive voltage to the pipe member 230to obtain processed data.

The vertical scale of the trace 290 thus corresponds to changes intime-resolved impedance resulting from the subtraction of two sets ofraw data representing return signals. The horizontal scale is calibratedin feet based on the wave propagation speed of the pipe measured usingthe calibration marker as described with reference to FIG. 23A. Forreference, FIG. 24 further includes a trace 292 that illustrates theprocessed data obtained using the marker element 284 as described above.The trace 292 illustrates an impedance change for the calibration markerlocated at the third test location 248.

The trace 290 illustrates a first impedance change at a trace portion290 a and a second impedance change at a trace portion 290 b. Theseimpedance changes generally correspond to the locations fifty feet andseventy five feet, respectively, from the far side 236. These impedancechanges thus illustrate that the test system 220 of the presentinvention detects and identifies corrosion at on the conductive member222 from a remote location.

Raw data was similarly taken with the test system 220 configured asillustrated in FIG. 23C. In FIG. 23C, the pulse source 272 of theexciting system 268 selectively launches one or more electromagneticpulses from the near side 234 such that the electromagnetic pulsespropagate at least from the near side 234 towards the far side 236. Whenappropriate, the DC power supply 278 of the perturbation system 270perturbs the conductive member 222 by selectively applying one or moreDC voltage levels and/or polarities to the conductive member 222 at thefar side 236.

As in the case depicted in FIG. 23B, the operation of the pulse source272 is timed in relation to the operation of the DC power supply 278such that the signal monitor 274 collects sets of raw data generatedunder different operating conditions of the test system 220.

Referring now to FIG. 25 of the drawing, that figure contains a datatrace 294 of the data obtained using the test system 220 configured asshown in FIG. 23C. The data trace 294 represents samples of the returnsignals detected with the DC power supply off subtracted fromcorresponding return signals detected with the DC power supply set to apositive voltage. Processed data is obtained by subtracting the returnsignal detected with the DC power supply off from the return signaldetected with the DC power supply applying a positive voltage to thepipe member 230. For reference, FIG. 24 further includes a trace 296that illustrates the processed data obtained using the marker element284 as described above. The trace 296 illustrates an impedance change at296 a for the calibration marker located at the third test location 248.

The trace 294 illustrates a first impedance change at a trace portion294 a and a second impedance change at a trace portion 294 b. Theseimpedance changes generally correspond to the locations fifty feet andseventy five feet, respectively, from the far side 236. These impedancechanges corroborate the conclusions reached from analyzing the trace 290as described above. FIG. 26 thus further supports the conclusion thatthe test system 220 of the present invention detects and identifies,from a remote location, corrosion on the conductive member 222.

The delay in the amount of time that it takes to polarize and depolarizethe conductive member can also be used to detect areas of corrosion. Asgenerally described above, the Applicants have discovered that thecorroded sections polarize and depolarize at a different rate than clearpipe with no corrosion. FIG. 26 contains three traces 298 a, 298 b, and298 c representing data measured using the test system 220 to illustrateremote activation of a corrosion patch on steel pipe under threedifferent bias conditions. These traces 298 a, 298 b, and 298 c arecompared in FIG. 26 to a trace 298 d associated with a marker element284 as depicted in FIG. 23A.

These traces 298 a, 298 b, and 298 c illustrate detection of corrosionby subtraction of pairs of waveforms taken at different times. The trace298 a illustrates impedance change data measured after three minutes ofnegative polarity subtracted from impedance data associated with abaseline reference taken prior to negative polarization. Trace 298 ashows a relatively severe increase in slope at the location of knowncorrosion anomalies as compared to a relatively flat slope prior to thelocation of the corrosion anomaly.

Trace 298 b illustrates impedance change resulting from depolarizationby subtracting measurements taken at three minutes of depolarizationfrom the baseline reference measurements taken prior to depolarization.Trace 298 a shows a decrease in slope after a slow increase in slopeprior to the location of known corrosion anomalies.

Trace 298 c illustrates impedance change resulting from positivepolarization subtracting measurements taken after three minutes ofpositive polarization from a base line trace measurements taken prior topositive polarization. Trace 298 c shows a slight decrease in slopeafter a relatively flat to increase in slope prior to the location ofknown corrosion anomalies.

The foregoing discussion illustrates that the signals generated by theexciting system 268 may be combined with signals generated by theperturbation system 270 in various ways to obtain data associated withanomalies in elongate conductive members.

1. A method of analyzing a conductive member for the presence ananomaly, comprising the steps of: applying a perturbation to theelongate conductive member to place the conductive member in a perturbedstate, where the electromagnetic characteristics of the conductivemember at the anomaly are altered when the conductive member is in theperturbed state; when the conductive member is in the perturbed stated,applying a test source signal to a first test location on the elongateconductive member remote from the corrosion to cause the test sourcesignal to travel along the pipe through the anomaly; detecting at leastone test return signal caused by the test source signal travelingthrough the anomaly; and analyzing the at least one test return signalfor characteristics associated with the anomaly.
 2. A method as recitedin claim 1, in which the elongate conductive member is in an unperturbedstate prior to the application of the perturbation, further comprisingthe steps of: when the conductive member is in the unperturbed stated,applying a reference source signal to the first test location to causethe reference source signal to travel along the pipe through theanomaly; detecting at least one reference return signal caused by thereference source signal traveling through the anomaly; and comparing theat least one reference return signal with the at lest one test returnsignal for characteristics associated with the anomaly.